SAN BRUNO, Calif.—Federal investigators probing last week's massive gas explosion here found an unusually built section of pipe in the ruins, focusing attention on the pipeline operator's inspections.

The operator, PG&E Corp., was midway through a federally mandated program to inspect and make emergency repairs to its most important gas-transmission pipelines—especially those that pass through populated areas such as San Bruno—when the explosion happened, killing at least four residents.

Authorities said Sunday afternoon the death toll was still officially four, though they found additional skeletal remains. The San Mateo County coroner said his office needed to run tests to determine how many bodies there are and if they are human.

Four people remain missing, local officials said. Police said they were continuing to search the devastated area for more bodies. The flames left 58 houses destroyed or uninhabitable, officials said.

The blast, which erupted just after 6 p.m. on Sept. 9, threw a section of pipe 100 feet away—a section that National Transportation Safety Board investigators said might hold clues to what caused the blast that left a 167-by-26-foot crater.

The 28-foot length of pipe consisted of several smaller segments that were welded together in an unusual configuration. It also contained a long seam that ran the length of the pipe, the NTSB said.

ENLARGE

The remains of burned vehicles and homes Saturday dotted the site of Thursday's explosion and fire, which killed at least four people.
Reuters

Officials said it was too early to say whether the pipe may have been weakened by the seam and welds or even whether it was typical of pipes used in the natural-gas pipeline owned by PG&E, a utility based in San Francisco that provides service to 15 million Californians.

NTSB Vice Chairman Christopher Hart said it was "still too early to tell" what role, if any, the pipe section may have caused in the blast, adding that the agency will send it to a Washington, D.C., lab for testing.

Investigators look closely at welds and seams because corrosion can attack these points, making them more vulnerable. A 2008 report commissioned by the Pipeline and Hazardous Materials Safety Administration, the federal safety regulator of gas-transmission pipelines, concluded that corrosion at seams can occur with little obvious damage to adjacent areas and that such flaws can precipitate a leak or rupture. The report specifically cited a certain type of pre-1971 pipe as being particularly susceptible to this problem. It isn't known if the San Bruno pipe was this type or had any corrosion, but it was of the same vintage and had a seam.

ENLARGE

It is not known how many similar sections of pipe may be buried beneath populated areas, but Mr. Hart said that it was "not necessarily" contrary to any rules or safe practice standard to use this type of pipe.

The San Bruno pipeline failure was the type of disaster that the federally mandated program sought to forestall, so much attention will now focus on whether PG&E was adequately carrying out the inspections.

In 2004, the PHMSA ordered all big firms owning gas-transmission lines—the biggest lines that carry the most gas and are under the greatest pressure—to do "risk-based assessments" that take into account the special dangers posed by high-pressure lines that carry gas under heavily populated areas.

The agency required utilities to make special assessments concerning whether they should take additional measures to protect the public, including installing heavier pipe, automatic shutoff valves and computerized leak-detection systems.

It appears that none of the special measures was taken in the case of the pipeline that exploded in San Bruno, Calif., although the utility said it had undergone regular inspections.

The NTSB's Mr. Hart said the utility had only manual shutoff valves on each end of the line. Asked if the utility should have upgraded to automatic valves, he said "that's one of the questions we'll be looking at."

Four people were killed and 39 others were injured after a massive explosion caused a devastating fire in San Bruno, California. Video courtesy of Fox News.

A PG&E official said the line was last inspected in March, when the utility conducted a gas-leak test.
Geisha Williams,
senior vice president of energy delivery, said it also was inspected as part of the federal program in November 2009, a process that included an examination for external corrosion. She said it was subject to aerial surveillance, at least quarterly, in which trained personnel look for dead vegetation along a pipeline's path, an indicator of a gas leak.

Documents filed by the utility with state regulators in 2009 say PG&E was preparing to do a more thorough inspection of the line in 2013, using a special probe to determine things like pipe thickness and detect corrosion. Older pipelines, like the one in San Bruno, must be re-engineered before they can accommodate a probe and PG&E estimated it would cost $14 million to inspect the 32-mile length of Line 132.

On Sunday, the California Public Utilities Commission told the utility to preserve all records related to the pipeline and any work or inspections related to it and to do special tests of its transmission lines. Given the difficulty of doing that, it's not clear what compliance will mean. Federal regulators said the utility was complying completely, as it did in 2008 after a much smaller pipeline explosion that killed one person and destroyed the victim's home.

Several people living near last week's explosion site said they smelled gas in the weeks before the blast. Irene Franco, 58, said she smelled it on two recent evenings, once three weeks ago and again on Tuesday, two days before the blast. "It was faint," she said.

Mr. Hart said his team was looking into the reports. He didn't know if the utility had responded to gas-leak complaints. PG&E's Ms. Williams said the company was reviewing what calls it had received and would turn them over to the NTSB.

Mr. Hart said usually when there is a large pipeline in a residential area, it means the pipe was buried before homes were built. As a consequence, people often are unaware their homes are astride a pipeline corridor, especially that of a big pipeline which would be buried many feet below the surface. Many residents said they didn't know the pipeline existed.

Installing an automatic shutoff valve might have helped reduce damage. Fire officials said the utility appeared to have difficulty shutting the flow of gas in the 30-inch-diameter pipeline, once the explosion ripped through the neighborhood. San Bruno Fire Chief Dennis Haag estimated it took an hour or more to stop the gas, and the resulting fire burned all night. PG&E didn't return a call seeking comment on the valve issue.

In its most recent filing with the PHMSA, PG&E said that it had completed special inspections of 1,417 miles of the 5,722 miles of pipeline it owns that were covered by the program, as of June 30. However, it said it had inspected 722 miles of the 1,021 miles of pipes that went through populated areas.

In the course of its inspections, it found 36 leaks and said they mostly were caused by corrosion and equipment failure. It said 28 lines suffered failures and two resulted in "incidents" that weren't identified.

PG&E's Ms. Williams said the utility was developing a process to inspect pipelines in its service territory. The utility recently asked for a rate increase and proposed to increase its spending on inspections so it could meet its 2012 deadline for the PHMSA program.

A tentative agreement has been reached . Under the settlement, which has not yet been approved by the full commission, the utility will raise rates by $67.3 million in 2011 to $529.1 million for its transmission and storage system. That sum includes funds earmarked for pipeline inspections, according to documents filed with the state utilities commission. PG&E spent $15 million on inspections in 2008 and expected to spend $17.5 million in 2009 and 2010 and $25.6 million in 2011 as it raced to meet its 2012 inspection deadline under the federal program.

Fire Tears Through San Francisco Suburb

"I'm just relieved we gave them all the money they wanted for inspections," said
Mike Florio,
an attorney and gas-pipeline expert who works for the Utility Reform Network, a ratepayer advocacy group in San Francisco. "They had a huge amount of deferred maintenance."

Among the confirmed dead were Jacqueline Greig, a ratepayer advocate for the Public Utilities Commission, who specialized in natural-gas issues, and one of her daughters, 13-year-old Janessa.

"We're in a state of shock," Mr. Florio said.

Authorities on Sunday afternoon allowed displaced residents to return to the roughly 300 houses that suffered little or no damage. On Fairmont Drive, neighbors pulled into their driveways and hugged each other. They compared how the heat from the flames warped car bumpers and house gutters.

"It's better than I expected," said Jadwindar Singh, 30, after he emerged from his two-story house. The heat broke two side windows and cracked his Toyota Corolla's windshield. Everything else, including the backyard wooden slide and swing set for his 1-year-old son, Nishaan, was intact.

That wasn't the case three homes downhill, beyond the police barricade. For more than a block stood only houseless chimneys, towering over a sea of ash.

"It's just overwhelming," Mr. Singh said as he videotaped the destruction. "It's just so close, and I have to see it everyday. Just four houses down, everything is gone."

Corrections & Amplifications A natural-gas-pipeline explosionin San Bruno, Calif., occurred on Sept. 9. An earlier version of this article incorrectly said that it happened on Aug. 9.

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